The overall goals of the laboratory are to investigate the development and function of mononuclear phagocytes in both normal and pathologic conditions. In the current project, combined electron microscopic and cytochemical techniques will be used to study the function of mononuclear phagocytes in certain pathologic processes. The areas to be investigated include the following: 1. The differentiation of macrophages into epithelioid and giant cells in chronic granulomata; 2. The differentiation of the activated macrophage; 3. The function of the mononuclear phagocyte in the humoral immune response; 4. The lysosomal pathways in mononuclear phagocytes of various tissues.